Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70058—Mask illumination systems
  • G03F7/70091—Illumination settings, i.e. intensity distribution in the pupil plane or angular distribution in the field plane; On-axis or off-axis settings, e.g. annular, dipole or quadrupole settings; Partial coherence control, i.e. sigma or numerical aperture [NA]
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
  • G01N21/956—Inspecting patterns on the surface of objects
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
  • G03F1/38—Masks having auxiliary features, e.g. special coatings or marks for alignment or testing; Preparation thereof
  • G03F1/44—Testing or measuring features, e.g. grid patterns, focus monitors, sawtooth scales or notched scales
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
  • G03F1/68—Preparation processes not covered by groups G03F1/20 - G03F1/50
  • G03F1/82—Auxiliary processes, e.g. cleaning or inspecting
  • G03F1/84—Inspecting
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/20—Exposure; Apparatus therefor
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
  • G01N21/956—Inspecting patterns on the surface of objects
  • G01N2021/95676—Masks, reticles, shadow masks

Definitions

• the invention concerns an illumination system and a projection objective of mask inspection apparatus.
• Microlithography is used for the production of microstructured components such as for example integrated circuits or LCDs.
• the microlithography process is carried out in what is referred to as a projection exposure apparatus having an illumination system and a projection objective.
• a projection exposure apparatus having an illumination system and a projection objective.
• Mirrors are used as optical components for the imaging process in projection objectives designed for the EUV range, that is to say at wavelengths of for example about 13 nm or about 7 nm, due to the lack of availability of suitable translucent refractive materials.
• the problem which inter alia arises in practice is that, depending on the respective form of the defects and the position thereof relative to the structure to be imaged, in the mask, deviations which are difficult to predict occur in the imaging process. Therefore direct analysis of the imaging effect of possible defect positions is desirable for minimising the mask defects and for implementing successful mask repair. There is thus a need for the mask to be quickly and easily tested, more specifically as far as possible under the same conditions as occur really in the projection exposure apparatus.
• an object of the present invention is to provide an illumination system and a projection objective of a mask inspection apparatus, which permit more accurate emulation of the conditions occurring in the projection exposure apparatus. That object is attained by the features of the independent claims.
• the invention concerns an illumination system of a mask inspection apparatus, wherein the illumination system in operation of the mask inspection apparatus illuminates a mask with an illumination bundle of rays which has a centroid ray, wherein said centroid ray has a direction dependent on the location of the incidence of the illumination bundle of rays on the mask.
• centroid ray' is used in accordance with the usual terminology to denote the energy mean over all subrays of a beam.
• centroid ray of the illumination bundle of rays is of a direction dependent on the location of the incidence of the illumination bundle of rays on the mask makes it possible, as explained hereinafter, for the pupil illumination of the projection objective to be more exactly emulated.
• the reference to a variation in the direction of the centroid ray in dependence on the location on the mask is preferably used to denote a variation in respect of which the maximum angle between the centroid rays of two bundle of rays which are incident on different locations on the mask is at least 1 °.
• the maximum angle between the centroid rays of two bundles of rays incident on different locations on the mask is at least 3°, in particular at least 5°, further particularly at least 10° and further particularly at least 15°.
• the maximum angle between the planes of incidence of two bundles of rays incident on different locations on the mask is at least 3°, in particular at least 5°, further particularly at least 10° and further particularly at least 15°.
• a mask which is analysed in operation of the mask inspection apparatus is designed for use with an illumination region, in the shape of a segment of a ring, in a projection exposure apparatus.
• the entire mask is scanned by a scanner slot which in the case of conventional (VUV) systems is typically of a rectangular geometry but which in the case of EUV systems is of a geometry in the shape of a segment of a ring.
• the EUV optical system has a rotationally symmetrical optical design, but in the lithography process only a small portion of that annular field is used, which is comparatively far away from the optical axis.
• the illumination bundle of rays it is known that to separate the illumination system and the projection objective it is necessary for the illumination bundle of rays to be directed at a finite angle of incidence on to the mask or the reticle, in which case (without the invention being restricted thereto) a typical angle in respect of the centroid ray relative to the surface normal on the mask can be 6° in present scanners.
• Figures 1 through 3 each show an object field 1 10 in the shape of a segment of a ring, on a mask 101 having a region 102 with structures to be imaged.
• the position which is currently being illuminated is at the center of the object field 1 10
• the position which is currently being illuminated in Figure 2 is in the region of the left-hand edge of the object field 1 10 and in Figure 3 it is in the region of the right-hand edge thereof. Consequently the projection objective also receives the light or observation bundle of rays with a principal ray angle (or chief ray angle) which is of the same value in relation to the surface normal of the mask 101 .
• optical system in the scanner and in particular in the projection optical system is of a rotationally symmetrical configuration, that angle, for reasons of symmetry, must always be in that plane formed by the object point which is just being observed of the mask 101 (or the object plane of the projection optical system), with the optical axis.
• the bundle of rays reflected at the object point which is respectively being observed is also incident in the projection objective at a (principal ray) angle (in the present example, 6°), but that angle is now so oriented that it is in that plane that is formed with the optical axis of the projection objective.
• a (principal ray) angle in the present example, 6°
• the rays passing into the projection objective do not all extend approximately parallel to each other, but rather are always perpendicular to the object field 1 10 in the shape of a segment of a ring, as can be seen from Figures 1 through 3.
• a movement along the object field 1 10 in the shape of a segment of a ring requires the above-described plane also to be turned therewith.
• the variation in the direction of the centroid ray, that is dependent on the location of incidence of the illumination bundle of rays on the mask complies with the following condition:
• R denotes the radius of the ring field
• the illumination system is designed for operation in the EUV mode.
• implementation is effected in a mask inspection apparatus designed for EUV, the invention is not restricted thereto.
• the invention can also be applied to a mask inspection apparatus of a higher working wavelength (for example 1 93 nm) as angle differences in illumination can also occur in relation to such wavelengths so that improved mask inspection can possibly also be achieved by the variation according to the invention in the direction of the centroid ray in dependence on the location on the mask.
• the invention can be carried into effect both in connection with systems involving a convergent configuration for the principal rays (that is to say the principal rays pass after reflection at the mask towards the optical axis) and also in systems involving divergent principal rays.
• Systems in which the principal rays pass divergently into the projection objective are known for example from US 2005/0088760 A1 (see Figures 91 and 93 of US 2005/0088760 A1 ).
• the variation in the direction of the centroid ray, that is dependent on the location of incidence of the illumination bundle of rays on the mask is such that the magnitude of the angle between the centroid ray and the surface normal on the mask is maintained.
• at least one blade (or aperture stop) which is movable in a predetermined plane of movement to adjust the variation in the direction of the centroid ray, that is dependent on the location of incidence of the illumination bundle of rays on the mask.
• the blades discussed here and hereinafter can be in the usual way in the form of disks or plates which are provided with holes designed in accordance with the desired illumination setting and which in other respects are non-transmitting.
• the invention however is not restricted thereto.
• EUV polarising elements
• the blade itself can also be variable in its shape, for example by virtue of an iris (or iris blade).
• an iris or iris blade
• another suitable device for adjusting the direction of incidence of the illumination rays for example a per se known multi-mirror array (referred to as an MMA), with a multiplicity of (micro)mirror elements which are adjustable differently from each other.
• MMA per se known multi-mirror array
• the above-mentioned predetermined plane of movement is in substantially coplanar relationship with the plane of the mask.
• region of the plane of movement, over which the blade is movable for adjustment of the variation in the direction of the centroid ray, that is dependent on the location of incidence of the illumination bundle of rays on the mask has a substantially reniform contour.
• the blade is designed for adjustment of one or more of the following illumination settings; quadruple illumination setting, dipole illumination setting, annular illumination setting, conventional illumination setting.
• conventional illumination setting is used to denote circular illumination with an intensity which is as uniform as possible within the circle.
• the blade is arranged rotatably, which can be advantageous depending on the respective specific configuration of the projection exposure apparatus to be emulated.
• the blade is in the form of a variably adjustable blade arrangement, wherein a substructure can be preserved in the brightness distribution of an illumination pupil of an EUV projection exposure apparatus, by adjustment of that blade arrangement.
• the blade arrangement has at least two blades movable relative to each other. Those blades can have in particular blade openings of differing shape and/or sizes. Alternatively or additionally one of those blades can have an apodising arm.
• the mask is arranged rotatably.
• the invention also concerns a projection objective of a mask inspection apparatus, wherein in operation of the mask inspection apparatus the projection objective observes a mask with an observation bundle of rays having a principal ray, wherein that principal ray has a direction dependent on the starting location of the observation bundle of rays on the mask.
• region of the plane of movement, over which the blade is movable for adjustment of the variation in the direction of the principal ray, that is dependent on the starting location of the observation bundle of rays on the mask has a substantially reniform contour.
• plane of movement extends in substantially coplanar relationship with the plane of the mask.
• the invention also concerns a mask inspection apparatus having an exposure system and a projection objective having the above- described features.
• a blade of the illumination system and a blade of the projection objective are movable in mutually synchronous relationship in opposite directions.
• the invention also concerns a method of operating a mask inspection apparatus, wherein in operation of the mask inspection apparatus the illumination system illuminates a mask with an illumination bundle of rays having a centroid ray and wherein the projection objective observes said mask with an observation bundle of rays having a principal ray, wherein the direction of the centroid ray and the direction of the principal ray are respectively varied in dependence on the location on the mask.
• the illumination pupil in its brightness distribution, has substructures deviating from an idealised form (which typically forms the basis in respect of dipole or quadrupole illumination settings).
• a substructure can be governed in particular by using in the illumination system a honeycomb condenser generating a multiplicity of light passages which are superposed in the plane of the mask. Those light passages now do not completely fill the pupil so that it is possible to see individual spots or 'illumination peaks'.
• the invention concerns an illumination system of a mask inspection apparatus, wherein the illumination system has at least one blade arrangement which is variably adjustable in such a way that, by adjustment of that blade arrangement, a substructure can be preserved in the brightness distribution of an illumination pupil of an EUV projection exposure apparatus.
• the blade arrangement has at least two blades movable relative to each other.
• Those blades can have in particular blade openings of differing shape and/or sizes.
• one of those blades can have an apodising arm.
• FIG. 1 - 5 show diagrammatic views to illustrate and explain the principle of the present invention
• Figure 6 shows a diagrammatic view of a mask inspection apparatus which is designed for EUV and in which the invention is carried into effect
• FIGS. 7a -7b show further diagrammatic views to explain the invention.
• FIGS 8 - 1 1 show diagrammatic views to explain embodiments in accordance with a further aspect of the invention.
• the mask inspection apparatus 600 includes an illumination system 610 and a projection objective 620, wherein light of an EUV light source 601 passes into the illumination system 610 and an illumination bundle of rays 615 is directed on to a respectively illuminated region or the object field of a mask 630 arranged in the object plane of the projection objective 620, and wherein that object field is imaged (by way of an observation bundle of rays 625) on to a camera (CCD sensor arrangement) 640 by means of the projection objective 620.
• a camera CCD sensor arrangement
• a respective blade 650 and 660 is used both in the illumination system 610 and also in the projection objective 620 of the mask inspection apparatus 600, as described hereinafter; the respective blade 650 and 660 respectively is movable in a predetermined plane of movement to adjust the variation in the direction of the centroid ray, that is dependent on the location of the incidence of the illumination bundle of rays 615 on the mask 630.
• Those blades 650, 660 are in turn preferably respectively placed in a pupil plane and respectively moved in a lateral direction (that is to say in the x- direction and the y-direction in the illustrated co-ordinate system).
• the respective centroid ray is influenced by means of blades 650, 660 in the illumination system 610 and the projection objective 620 respectively.
• the angle of the illumination optical system (that is to say the angle of the centroid ray of the illumination bundle of rays incident on the mask) is adjusted by way of the position of the blade 650 provided in respect of the illumination system 620, and the angle of the centroid ray or main ray of the (observation) bundle of rays in the imaging ray path, which passes into the projection objective, is adjusted by way of the position of the blade 660 provided in respect of the projection objective.
• the other components of the illumination system 610 and the projection objective 620 do not have to be moved for that purpose.
• the planes of movement in which the two blades 650, 660 are moved extend parallel to and in coplanar relationship with the mask plane respectively (without the invention being restricted thereto).
• the blade 650 has openings 651 through 654 corresponding to the desired illumination setting (in the illustrated example a quadrupole illumination setting) and is moved in a plane of movement in accordance with the desired angle which is to be set, that plane of movement in the illustrated example being parallel to the plane of the mask.
• Reference '410' denotes a region which is used in the course of the entire movement of the blade 650 and which as shown in Figure 4 can be of a reniform geometry.
• the reniform region 410 thus also represents the region which prior to use of the blade 650 must be filled with light if or before the blade 650 comes into operation. That signifies that the optical system is generally designed for a larger angular region (that is to say a larger numerical aperture).
• Figure 5 shows the similar situation for the blade 660 which as shown in Figure 6 is used in the projection optical system of the mask inspection apparatus but which has a circular geometry and which in turn is similarly moved in the pupil plane of the projection optical system of the mask inspection apparatus (projection objective 620).
• the optical axis of the projection optical system of the scanner which extends perpendicularly to the plane of the paper, is identified by OA p .
• the Figure also shows the scanner slot or the object field 631 which is in the shape of a segment of a ring and which extends concentrically around the optical axis OA p (so that the optical axis OA p is at the center point of curvature of the object field 631 in the shape of a segment of a ring).
• Figure 7a also indicates both for the left-hand and the right-hand edge and also for the center of the object field in the shape of a segment of a ring, the respective configuration of the plane of incidence ' ⁇ ', 'B' and 'C respectively which each also extend perpendicularly to the plane of the paper and intersect the optical axis OA p .
• the blades 650 and 660 which are disposed in the pupil plane of the illumination system and the projection objective respectively (that is to say the projection optical system of the mask inspection apparatus) and implement the respective configuration of the plane of incidence ' ⁇ ', ' ⁇ ', and 'C according to the invention are indicated here as a plan view.
• Figure 7b shows a corresponding side view in which OA M denotes the optical axis of the mask inspection apparatus, wherein the object field 631 in the shape of a segment of a ring (to be seen in cross-section here) is disposed at a spacing R from the optical axis of the projection exposure apparatus and is of the width b.
• the blades in the illumination system or projection objective respectively are here denoted by ASm and AS 0b respectively.
• the invention is thus based on the concept, during the movement of the mask 630 in the course of mask inspection, to simulate the effective direction of incidence of the light, which in the embodiment described here is effected by the blades 650, 660 arranged in the illumination system 610 and the projection objective 620 (projection optical system) of the mask inspection apparatus respectively also being moved.
• the blades 650, 660 are moved over the mask in such a way that depending on the respective mask location which is currently being inspected, different directions of the centroid ray are set in relation to the optical axis. Therefore the blade movement achieves precisely the desired variation in location of the centroid ray, wherein the illumination setting is respectively maintained as a consequence of using the same blade.
• the blades 650, 660 each to be arranged at a relatively large spacing relative to the mask 630 and as diagrammatically shown in Figure 6 to be disposed outside the remainder of the optical arrangement of the illumination system 610 and the projection objective 620 respectively (that is to say the projection optical system of the mask inspection apparatus), in which respect in particular there does not have to be any additional imaging optical means between the blade 650 and the blade 660 respectively and the illumination system and the projection objective respectively (projection optical system of the mask inspection apparatus).
• the invention however is not restricted thereto so that in other embodiments a further (imaging) optical system can also be provided between blade and illumination system or projection optical system of the mask inspection apparatus.
• a mathematical description of the variation according to the invention in the centroid ray in dependence on the location on the mask can be as follows: if x and y are used to denote the co-ordinates of the mask plane and y is used to denote the co-ordinate perpendicular to the mask plane, and if in that respect x is used to denote the co-ordinate along which scanning is effected, the active surface of the mask extends in the y-direction from -b/2 through +b/2, wherein b denotes the scanner slot width (which can be of a value by way of example of 104 mm).
• c z corresponds to the cosine of the angle of incidence which can involve typical values of at the present time between 6° and about 8 - 9° or thereabove (for higher numerical apertures).
• FIG. 9 refers to Figures 9 through 1 1 to describe embodiments which serve to reproduce the above-described parcellings of the pupil illumination including the fluctuations in intensity in mask inspection.
• a blade arrangement comprising at least two blades (in further embodiments therefore also three, four or more blades) is used, wherein those blades are so-to-speak 'connected in series' and are of such a design configuration that relative displacement and/or rotation of the blades makes it possible to adjust the effective opening of the pupil parcels and thus the integral brightness or light efficiency thereof.
• the blade arrangement is made up of two blades 910, 920 which are arranged in succession in the light propagation direction and which each have three holes 91 1 - 913 and 921 - 923 respectively (for example a respective hole for each pupil parcel), wherein however both blades 910, 920 have holes of differing shape.
• the first blade 1 10 which is shown only diagrammatically and by way of example has three circular holes 91 1 - 913, whereas the second blade 920 has a circular hole 922 between two elongate holes 921 and 923.
• the individual blades of the blade arrangement do not necessarily have to be arranged in directly successive relationship.
• FIG. 10 it is also possible to provide a variable hole size and thus a variation in the effective opening of the pupil parcels and thus the integral brightness or light efficiency, by at least one blade of at least two blades 950, 960 having at least one apodising arm (here the second blade 960 shown in Figure 10b) which partially covers the hole opening and thus leads to an effective reduction in the size of the hole.
• the effective hole size is altered passage-wise by relative displacement of the second blade 960 relative to the first blade 950 in Figure 10a, by the hole size in the first blade 950 being reduced by the area of the arm covering it.
• Figure 1 1 is a merely diagrammatic view showing further possible configurations of an arm on a blade 970.
• a blade arrangement for variable adjustment of the intensity in the above-described subpupils or substructures can also be implemented in a (single-stage) blade having a multiplicity of variably adjustable iris blades which are adjustable individually or in their entirety by suitable actuators.
• the above-described concept of providing the complete 'substructured' illumination distribution within the mask inspection apparatus can also be implemented independently of the concept according to the invention of varying the direction of the centroid ray in dependence on the location on the mask.
• the invention also concerns a mask inspection apparatus in which a substructure of the illumination distribution is afforded, preferably by using a suitable blade arrangement, without at the same time the variation in the direction of the centroid ray in dependence on the location on the mask also being implemented.

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• 2010
  • 2010-02-22 DE DE102010009022.0A patent/DE102010009022B4/de active Active
• 2011
  • 2011-02-15 WO PCT/EP2011/052184 patent/WO2011101331A1/en active Application Filing
  • 2011-02-15 JP JP2012554285A patent/JP5616983B2/ja active Active
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• 2012
  • 2012-08-16 US US13/587,077 patent/US10114293B2/en active Active

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